Label-free analysis of breast tissue polarity by Raman imaging of lipid phase.

The formation of the basoapical polarity axis in epithelia is critical for maintaining the homeostasis of differentiated tissues. Factors that influence cancer development notoriously affect tissue organization. Apical polarity appears as a specific tissue feature that, once disrupted, would facilitate the onset of mammary tumors. Thus, developing means to rapidly measure apical polarity alterations would greatly favor screening for factors that endanger the breast epithelium. A Raman scattering-based platform was used for label-free determination of apical polarity in live breast glandular structures (acini) produced in three-dimensional cell culture. The coherent anti-Stokes Raman scattering signal permitted the visualization of the apical and basal surfaces of an acinus. Raman microspectroscopy subsequently revealed that polarized acini lipids were more ordered at the apical membranes compared to basal membranes, and that an inverse situation occurred in acini that lost apical polarity upon treatment with Ca(2+)-chelator EGTA. This method overcame variation between different cultures by tracking the status of apical polarity longitudinally for the same acini. Therefore, the disruption of apical polarity by a dietary breast cancer risk factor, ω6 fatty acid, could be observed with this method, even when the effect was too moderate to permit a conclusive assessment by the traditional immunostaining method.